MONGOID-5823 Use proper thread-local variables instead of fiber-local variables (Backport to 9.0) #5896
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… variables (mongodb#5891) * MONGOID-5823 Use proper thread-local variables Using fiber-local variables instead of thread-local variables has the potential to introduce difficult bugs when Mongoid's internal state is not visible to Fiber-wrapped cascading callbacks. * remove cruft from an earlier experient * *grumble* rubocop *grumble* * fix test failures * compensate for jruby
comandeo-mongo
approved these changes
Oct 25, 2024
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(Backport from master to 9.0-stable)
MONGOID-5688 introduced a new way of processing cascading callbacks on embedded children, using Fibers to linearize the recursive calls. This proved very effective in avoiding
SystemStackErrorexceptions caused by large numbers of embedded documents.However, it turns out that
Thread#[]andThread#[]=get and set fiber-local variables, and not thread-local variables. Mongoid was using these methods quite a bit to set and manage its own internal state, which meant that any cascading callback on embedded children would be executed in a context that lacked all of Mongoid's state from the parent thread.This PR fixes this issue by changing Mongoid's state handling routines (
Mongoid::Threaded) to use actual thread-local storage (Thread#thread_variable_getandThread#thread_variable_set) instead of the fiber-local variables.